1. Field of the Invention
The present invention relates to the identification of bacteria and more particularly to a method and apparatus for identifying bacteria utilizing electro-optical investigation.
2. Description of the Prior Art
Numerous methods have been developed and are presently utilized to identify various bacteria for purposes ranging from disease detection and treatment, to microbial research. Classically, samples of material believed to contain a given bacterium are investigated by first developing a culture on an appropriate growth medium, after which the presence or absence of the bacterium in question may be determined by a variety of further tests. In the instance of disease detection, this procedure can be extremely time-consuming, and may prove crucial in lifethreatening situations.
Certain basic investigations have been conducted recently in the area of electro-optics, in an effort to learn more about the structure and function of materials by their behavior in polarized light. In particular, several studies by V. J. Morris et als., noted that the application of an electrical field to a suspension of essentially non-spherical bacteria, resulted in a partial orientation of the bacteria, believed due to the development of a strong, induced dipole moment on the bacteria by the electric field. Carrying this further, V. J. Morris et als., Biochimica et Biophysica Acta, 392:328-334 (1975), investigated the effect of certain antibiotics on the electrical polarizability of aqueous suspensions of E. coli, and found that substantial changes in polarizability, measured as a function of light-scattering effect, took place. The authors theorized that the antibiotic molecules, in this study neomycin and streptomycin, were absorbed onto the bacterial surface, and resultingly reduced the surface charge of the bacteria and its apparent induced dipole moment. Further studies by V. J. Morris et als. relating to this subject comprise V. J. Morris et als., Microbios, 17:133-139 (1976), and Biochimica et Biophysica Acta, 497:253-259 (1977).
In general, it is known that when living cells are disposed in a liquid and the liquid is placed in an external electrical field, the cells will align themselves in the field. This alignment takes place because the cells have an asymmetric distribution of electrical charge on their surfaces. The asymmetric distribution of electrical charge on the surface of the cells may be a fixed property of the cell, in which case the cell is referred to as permanent dipole, or may be induced on the surface of the cell by the presence of the external electrical field, in which latter instance such charge distribution is referred to as an induced dipole. This asymmetry was identified and further investigated by Morris et al., by use of lightscattering optical techniques that measured by birefringence of the bacterial cells, i.e. the separation of a beam of light into two unequally refracted, plane polarized light beams. Thus far, however, this phenomenon has exhibited utility as an investigative avenue only, for the purpose of determining the electrical consequences of surface interactions between various particles, including living cells.
The present invention therefore attempts to unite the described phenomenon with appropriate methodology to address the need for a rapid and accurate assay technique for the detection and enumeration of particular microbial cells.